persistent-template: Setting to not prefix fields with model names

As discussed on [the mailing list](https://groups.google.com/forum/#!topic/yesodweb/wA0ds3czz04)

I tried to do this for FKs as well (`CommentUserId` -> `UserId`) but I couldn't find how these names are prefixed, e.g. `[ConP (mkName $ unpack $ unHaskellName (entityHaskell t) ++ "Id") []]` where `t` is `CommentUser` already. Any pointers to where to make this change?